1. Field of the Invention
The present invention relates to a communication system which performs communication by use of the Internet protocol (IP).
2. Description of the Related Art
In recent years, the IP-based communications have been performed in many of the communication systems including the exchange systems and the mobile communication systems, and have been becoming more important. In the systems having the function of IP communication, it is necessary to perform operations for maintenance such as status monitoring and operational settings.
FIG. 13 is a schematic diagram illustrating an outline of a conventional IP communication system. The IP communication system 5 illustrated in FIG. 13 is constituted by an IP communication device 50 and an external maintenance terminal 50a, and the IP communication device 50 comprises a maintenance-and-operation board 51, a LAN (Local Area Network) switchboard 52, an external-LAN-interface board 53, and communication-processing boards 54-1 to 54-n.
The external-LAN-interface board 53 is an interface board arranged for connecting the IP communication device 50 to the external maintenance terminal 50a. The LAN (Local Area Network) switchboard 52 is a board arranged for switching connections between the above boards in the IP communication device 50. The maintenance-and-operation board 51 is a board arranged for performing maintenance and controlling operations of the IP communication device 50 by performing communication with the external maintenance terminal 50a. The communication-processing boards 54-1 to 54-n are boards arranged for performing various processing functions, e.g., call processing functions, and functions of a communication interface with other systems. The external maintenance terminal 50a is provided for an operator performing operations for maintenance such as status monitoring and operational settings.
Normally, the external maintenance terminal 50a is a communication device having a global address, and the IP communication device 50 is a device constituted by a plurality of boards each having a local address. Specifically, a global MAC (Media Access Control) address is assigned to the external maintenance terminal 50a, and a local MAC address is assigned to each of the boards (including the maintenance-and-operation board 51) in the IP communication device 50.
The global MAC address is a uniquely assigned public address, and the local MAC addresses are addresses assigned by a user. For example, the local MAC addresses are assigned on the basis of the installation positions of the slots or shelves.
Therefore, the address system of the IP communication device 50a is different from the address system of the boards in the IP communication device 50, so that the global MAC address of the external maintenance terminal 50a cannot be used in the IP communication device 50, and the external maintenance terminal 50a cannot be connected to (cannot communicate with) the IP communication device 50.
In conventional IP communication devices, a dedicated board having a function of translating a global MAC address into a local MAC address, and a local MAC address into a global MAC address is provided for the purpose of solving the above problem. Specifically, in the conventional IP communication system 5 of FIG. 13, the external-LAN-interface board 53 is provided for the above purpose.
Thus, when the external maintenance terminal 50a is connected to the maintenance-and-operation board 51 in the IP communication device 50 for communication with the maintenance-and-operation board 51, address translation is performed under software control of a CPU in the external-LAN-interface board 53 so that IP communication between the external maintenance terminal 50a (which is a global and external terminal) and the maintenance-and-operation board 51 (which is a local device in the IP communication device 50) is realized through the external-LAN-interface board 53.
For example, Japanese Unexamined Patent Publication No. 11-27310 (in Paragraph Nos. 0018 to 0028 and FIG. 1) discloses a conventional IP communication technique in which a global MAC address is translated into a local MAC address and a local MAC address is translated into a global MAC address.
However, the conventional IP communication system 5 has the following problems (1) to (4).
(1) When the external-LAN-interface board 53 fails, the connection between the external maintenance terminal 50a and the maintenance-and-operation board 51 is disconnected, so that it is impossible to send information on the failure in the system to the external maintenance terminal 50a until the external-LAN-interface board 53 recovers from the failure.
(2) The external-LAN-interface board 53 is fixedly interposed between the external maintenance terminal 50a and a board in the maintenance-and-operation board 51, and communication is performed under software control of the CPU in the external-LAN-interface board 53. Therefore, it takes substantial time to transfer massive files and collect log data indicating system failures, so that it is impossible to quickly perform maintenance.
(3) When massive data is transmitted between the external maintenance terminal 50a and the maintenance-and-operation board 51, the processing load imposed on the CPU in the external-LAN-interface board 53 increases, and excessive usage of the CPU can cause disconnection in the communication with the external maintenance terminal 50a. 
(4) Since provision of a dedicated board such as the external-LAN-interface board 53 is required for connection with the external maintenance terminal 50a, the equipment cost increases.